Keratitis-ichthyosis-deafness syndrome, atypical connexin GJB2 genemutation, and peripheral T-cell lymphoma: more than a random association?

Keratitis-ichthyosis-deafness (KID) syndrome is a rare congenital disorder characterized by a variety of skin lesions— that is, palmoplantar keratoderma, thickening of the skin, and erythematous verrucous lesions—neurosensorial hypoacusia, and keratitis with a variable degree of visual impairment. Both sporadic and familial forms of the syndrome have been described, the latter usually showing a dominant pattern of inheritance. The molecular lesion responsible for the syndrome typically involves the connexin 26 (Cx26) gene (GJB2). Most patients display the heterozygous c.148G→A mutation causing the substitution of an aspartic acid for an asparagine at position 50 (p.Asp50Asn), while a few of them show the c.50C→T mutation, implying the substitution of a serine for a phenylalanine at position 17 (p.Ser17Phe). However, even a mutation in the connexin 30 (Cx30) gene (GJB6) has been found in a typical KID patient, thus suggesting a genetic heterogeneity of the syndrome. As connexins are a large family of small integral membrane proteins which influence tissue cornification by modulating the establishment of direct cell-cell communication through gap junction channels, it is likely that defects involving this class of proteins are at the basis of the wellknown increased incidence of squamous cell carcinoma in KID patients

A Human-Derived Monoclonal Antibody Targeting Extracellular Connexin Domain Selectively Modulates Hemichannel Function

Connexin hemichannels, which are plasma membrane hexameric channels (connexons) composed of connexin protein protomers, have been implicated in a host of physiological processes and pathological conditions. A number of single point pathological mutations impart a "leaky" character to the affected hemichannels, i.e., make them more active or hyperactive, suggesting that normal physiological condition could be recovered using selective hemichannel inhibitors. Recently, a human-derived monoclonal antibody named abEC1.1 has been shown to inhibit both wild type and hyperactive hemichannels composed of human (h) connexin 26 (hCx26) subunits. The aims of this work were (1) to characterize further the ability of abEC1.1 to selectively modulate connexin hemichannel function and (2) to assess its in vitro stability in view of future translational applications. In silico analysis of abEC1.1 interaction with the hCx26 hemichannel identified critically important extracellular domain amino acids that are conserved in connexin 30 (hCx30) and connexin 32 (hCx32). Patch clamp experiments performed in HeLa DH cells confirmed the inhibition efficiency of abEC1.1 was comparable for hCx26, hCx30 and hCx32 hemichannels. Of note, even a single amino acid difference in the putative binding region reduced drastically the inhibitory effects of the antibody on all the other tested hemichannels, namely hCx30.2/31.3, hCx30.3, hCx31, hCx31.1, hCx37, hCx43 and hCx45. Plasma membrane channels composed of pannexin 1 were not affected by abEC1.1. Finally, size exclusion chromatography assays showed the antibody does not aggregate appreciably in vitro. Altogether, these results indicate abEC1.1 is a promising tool for further translational studies

Autosomal recessive and sporadic non syndromic hearing loss and the incidence of Cx26 mutations in a province of Iran

Despite the enormous heterogeneity of genetic hearing loss, mutations in the GJB2 (connexin 26) gene located on "DFNB1" locus (13q12) account for up to 50 of cases of autosomal recessive non-syndromic hearing loss (ARNSHL) in some populations. This study describes the analysis of 100 autosomal recessive and sporadic nonsyndromic hearing loss individuals from 79 families each having at least one deaf child in Chehar Mahal va Bakhtiari province in west of Iran. We have investigated the prevalence of the connexin 26 gene mutations using nested PCR strategy to screen the predominant 35delG mutation and subsequent direct sequencing to detect other Cx26 mutations. Seven different genetic variants were detected from which one novel variant was including 363delC. The 35delG was the most common mutation found in 5 of 79 families (6.3). Cx26 related deafness mutations (35delG,V27I; E114G) and R127H) were found in 12 of 158 chromosomes studied (7.8%). We conclude that the association of Cx26 mutations with deafness in Chehar Mahal va Bakhtiari province is low and looks like most other populations of Iran

Report of a new mutation and frequency of connexin 26 gene (GJB2) mutations in patients from three provinces of Iran

Autosomal recessive and sporadic non-syndromic hearing loss (ARSNSHL) is the major form of hereditary deafness. Mutations in the GJB2 gene encoding the gap-junction protein Connexin 26 have been identified to be highly associated with ARSNSHL. In this study we have analyzed 196 deaf subjects from 179 families having one or more deaf children in 3 proviences of Iran, including Kordestan, Khuzestan and Golestan. The nested PCR prescreening strategy and direct sequencing technique were used to detect the mutations in coding exon of the gene. Altogether 3 GJB2 recessive mutations including 35delG, 167delT and V27I+E114G, were identified in 23 of 179 families (12.8). Fourteen of 179 families were observed to have GJB2 mutation in both alleles (7.8). A novel variant (R159H) also was found in a deaf family from Khuzestan. Four polymorphisms V27I, E114G, S86T and V153 I also were detected in 7 families. A polymorphism(S86T) was seen in the whole population studied. Our data indicated that the rate of connexin 26 mutations is different in this three Irainian population and is lower than the high frequency of 35delG (26) reported from Gilan province in the north of Iran

Compartmentalized and signal-selective gap junctional coupling in the hearing cochlea

Gap junctional intercellular communication (GJIC) plays a major role in cochlear function. Recent evidence suggests that connexin 26 (Cx26) and Cx30 are the major constituent proteins of cochlear gap junction channels, possibly in a unique heteromeric configuration. We investigated the functional and structural properties of native cochlear gap junctions in rats, from birth to the onset of hearing [ postnatal day 12 (P12)]. Confocal immunofluorescence revealed increasing Cx26 and Cx30 expression from P0 to P12. Functional GJIC was assessed by coinjection of Lucifer yellow (LY) and Neurobiotin (NBN) during whole-cell recordings in cochlear slices. At P0, there was restricted dye transfer between supporting cells around outer hair cells. Transfer was more extensive between supporting cells around inner hair cells. At P8, there was extensive transfer of both dyes between all supporting cell types. By P12, LY no longer transferred between the supporting cells immediately adjacent to hair cells but still transferred between more peripheral cells. NBN transferred freely, but it did not transfer between inner and outer pillar cells. Freeze fracture further demonstrated decreasing GJIC between inner and outer pillar cells around the onset of hearing. These data are supportive of the appearance of signal-selective gap junctions around the onset of hearing, with specific properties required to support auditory function. Furthermore, they suggest that separate medial and lateral buffering compartments exist in the hearing cochlea, which are individually dedicated to the homeostasis of inner hair cells and outer hair cells

The p.Cys169Tyr variant of connexin 26 is not a polymorphism

Mutations in the GJB2 gene, which encodes the gap junction protein connexin 26 (Cx26), are the primary cause of hereditary prelingual hearing impairment. Here, the p.Cys169Tyr missense mutation of Cx26 (Cx26C169Y), previously classified as a polymorphism, has been identified as causative of severe hearing loss in two Qatari families. We have analyzed the effect of this mutation using a combination of confocal immunofluorescence microscopy and molecular dynamics simulations. At the cellular level, our results show that the mutant protein fails to form junctional channels in HeLa transfectants despite being correctly targeted to the plasma membrane. At the molecular level, this effect can be accounted for by disruption of the disulfide bridge that Cys169 forms with Cys64 in the wild-type structure (Cx26WT). The lack of the disulfide bridge in the Cx26C169Y protein causes a spatial rearrangement of two important residues, Asn176 and Thr177. In the Cx26WT protein, these residues play a crucial role in the intra-molecular interactions that permit the formation of an intercellular channel by the head-to-head docking of two opposing hemichannels resident in the plasma membrane of adjacent cells. Our results elucidate the molecular pathogenesis of hereditary hearing loss due to the connexin mutation and facilitate the understanding of its role in both healthy and affected individuals

An overview of the focus of the International Gap Junction Conference 2017 and Future Perspectives

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Dynamic changes in connexin expression correlate with key events in the wound healing process.

Wound healing is a complex process requiring communication for the precise co-ordination of different cell types. The role of extracellular communication through growth factors in the wound healing process has been extensively documented, but the role of direct intercellular communication via gap junctions has scarcely been investigated. We have examined the dynamics of gap junction protein (Connexins 26, 30, 31.1 and 43) expression in the murine epidermis and dermis during wound healing, and we show that connexin expression is extremely plastic between 6 hours and 12 days post-wounding. The immediate response (6 h) to wounding is to downregulate all connexins in the epidermis, but thereafter the expression profile of each connexin changes dramatically. Here, we correlate the changing patterns of connexin expression with key events in the wound healing process

Deafness–associated connexin 26 gene (GJB2) mutations in Iranian population

Mutations in the GJB2 gene at the DFNB1 locus on chromosome 13q12 are associated with autosomal recessive non syndromic hearing loss (ARNSHL) in many populations. A single mutation, at position 35 (35delG) accounts for approximately 30-63% of mutations in white populations with a carrier frequency of 1.5-2.5% in most European, North American and Mediterranean populations. In this study we have investigated the prevalence of the GJB2 gene mutations using direct sequencing in 43 presumed ARNSHL subjects from 34 families in an Iranian population. Eleven different genetic variants were identified. GJB2-related deafness mutations (35delG, 235delC, W24X, R184P and IVS1+1G>A) were found in 9 of 34 families (26.5%). The 35delG was the most common mutation found in 5 of 34 families (14.7%). We found one novel variant (–3517G>A) in the upstream region to the gene. The mutation frequency found in this study is lower than other ethnic groups with European ancestry, but it is indicating that mutation in GJB2 in Iranian population has contribution to ARNSHL. We have also developed a simple and accurate nested PCR assay to screen the 35delG mutation in 250 unrelated unaffected Iranian individual (controls). No 35delG heterozygous was found in the control population